Why pay that much money for a music catalog? Even if it does give Sony exclusive ownership of works by Bob Dylan, Eminem, Taylor Swift and The Beatles.

"An important, unrealized asset in this business is music publishing," said Paul Young, a music industry studies professor at USC's Thornton School of Music, "which is the ownership of a song copyright, as opposed to the recordings we're sometimes more familiar with."

"You're giving permission to use a song to not just a record company, but to a radio station, film company, tv company," said Young. Transactions that are far less threatened by music's digital revolution.

The music publishing business clearly remains lucrative, even when the music industry is struggling.

The show "Mad Men" reportedly paid $250,000 in licensing fees to use The Beatles song "Tomorrow Never Knows."

Publishing catalogs are attractive for a couple of reasons, said Jeff Jampol, the president of Jam, Inc., which manages musicians and their estates. "It's easy to see what they've done for the last ten, twenty, thirty years."